Loud speaker with actuating systems of different types



G. GRUSCHKE Dec. 6, 1932.

LOUD SPEAKER WITH AGTUATING SYSTEMS OF DIFFERENT TYPES Filed Sept. 4. 1929 INVENTOR v 1 M @Msamz BY Afioliu Y Patented Dec. 6, 1932 UNITED STATES PATENT OFFICE GEGRG GRUSCHKE, OF 'BERLIN-WILMERSDORF, GERMANY, ASSIGNOR T0 SIEMENS &

CORPORATION or GERMANY.

LOUD SPEAKER WITH ACTUATING SYSTEMS OF DIFFERENT TYPES Application filed September 4, 1929, Serial No. 390,239, and in Germany September 7, 1928.

The invention concerns loudspeakers which are to reproduce, as true to nature as possible, a wide frequency range without favoring individual frequency groups. The oscillations of the sound must be reproduced without distortion with respect to their absolute size as well as corresponding to the proportion of the sound intensity of the individual frequency bands.

The loudspeakers known in the prior art with a single actuating system emphasize especially certain frequency groups in the reproduction. The electromagnetic actuating systems, for instance, are very well adapted for the middle range frequencies, the electrostatic for the high frequencies and the electrodynamic for the low frequencies. These characteristic differentiating qualities have already been used to insure a natural pure reproduction of musical offerings in the manner that the talking currents were conveyed simultaneously to three loudspeakers separated from one another and operating accord ing to different principles, and disposed close together, for instance in a common housing. According to the invention several different actuating systems are combined in the manner that they influence a membrane which is common to all. By this means the loudspeaker may be kept down to a small size and to lighter weight. Disturbing interferences and surges are avoided for the reason that the sound waves are radiated from a common membrane in contrast to the arrangements known in the prior art.

The figures show an embodiment of the idea of the invention by way of example. The talking currents coming from the amplifier or from an electric sound box are conveyed to the-telescopic coil 1 of an actuating system 2 operating according to the electrodynamic princple. The conical membrane 4 is connected with the coil 1 by means of a small pin 3 and is covered by a mctallically conducting coating or is made of'metal en tirely. To the membrane 4 is applied, with the insertion of a flexible dielectric 5 a Second metallic layer 6. Both metallic coatings form, with the intermediate layer, a condenser whose one plate is movable and is,

with the variation of the electric field, more or less strongly attracted to the fixed plate.

Both plates are connected, if necessary, with the insertion of amplifiers or transformers, with the same current source which also supplies the telescoping coil of the electrodynamic system. The membrane 6 follows the oscillations of the'membrane 4 immediately since it operates practically inertialess. Over the forced oscillations, produced by membrane 4 which is excited by the-electrodynamic system, are superimposed the oscillations which have been impressed by, the talking currents upon the electrostatic system and whose middle and lower frequencies are quite strongly damped by the elastic dielectric, while the high frcquenci es with their smaller amplitude may oscillate freely. These high frequencies are lacking in the electrodynamic system since the latter, due to its relatively large'inertia, cannot, without retardation, follow the oscillations following one another in rapid succession. By means of the cooperation of the two systems there is created a loudspeaker which reproduces with uniform good quality the entire frequency range.

In similar manner the electromagnetic system may be combined with the electrostatic or electrodynamic systems.

In the reproduction of many muiscal oifer ings it is suitable to have the talking currents act upon one system only. I The lead-in conductors are, therefore, supplied with switches which interrupt the circuit of the talking current.

I claim:

1. An acoustic device comprising a vi bratile member having a conducting surface, means including a winding adapted to be traversed by a modulated electric current for vibrating said member, and a second conductin g surface electrosta'tically cooperating with the first mentioned conducting surface for causing additional vibration of said member.

2. An acoustic device comprising a vi-- bratile member consisting of a pair of conducting surfaces and an insulating medium therebeweteen, said conducting surfaces being adapted for movement relative'to each other,

find means for vibrating said vibratile memer.

3. An acoustic device comprising a pair of conducting surfaces insulated from each other and adapted to vibrate relative to each other, and means for vibrating said surfaces as a whole, said means includin a winding adapted to be traversed by acoustlcally modulated electrical currents.

In testimony whereof I aflix my signature.

' GEORG GRUSGHKE. 

